Procedure

     SPKR20 ( SPK, read record from segment, type 20 )

     SUBROUTINE SPKR20 ( HANDLE, DESCR, ET, RECORD )

Abstract

     Read a single SPK data record from a segment of type 20
     (Chebyshev, velocity coefficients only).

Required_Reading

     SPK

Keywords

     EPHEMERIS

Declarations

     IMPLICIT NONE

     INTEGER               HANDLE
     DOUBLE PRECISION      DESCR    ( 5 )
     DOUBLE PRECISION      ET
     DOUBLE PRECISION      RECORD   ( * )

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
     HANDLE     I   File handle.
     DESCR      I   Segment descriptor.
     ET         I   Evaluation epoch.
     RECORD     O   Data record.

Detailed_Input

     HANDLE,
     DESCR    are the file handle and segment descriptor for an SPK
              segment of type 20.

     ET       is an epoch for which a data record from the specified
              segment is required. ET is expressed as seconds past
              J2000 TDB.

Detailed_Output

     RECORD   is an array of data from the specified segment which,
              when evaluated at epoch ET, will give the state
              (position and velocity) of the target body identified
              by the input segment descriptor. The descriptor
              specifies the center of motion and reference frame of
              the state.

              The structure of the record is as follows:

                 +--------------------------------------+
                 | record size (excluding this element) |
                 +--------------------------------------+
                 | Coverage interval midpoint           |
                 +--------------------------------------+
                 | Coverage interval radius             |
                 +--------------------------------------+
                 | Coeffs for X velocity component      |
                 +--------------------------------------+
                 | Coeffs for Y velocity component      |
                 +--------------------------------------+
                 | Coeffs for Z velocity component      |
                 +--------------------------------------+
                 | X position component                 |
                 +--------------------------------------+
                 | Y position component                 |
                 +--------------------------------------+
                 | Z position component                 |
                 +--------------------------------------+

              In the above record

                 - Times are expressed as seconds past J2000 TDB.
                 - Position components have units of km.
                 - Velocity coefficients have units of km/s.

              RECORD must be declared by the caller with size large
              enough to accommodate the largest record that can be
              returned by this routine. See the INCLUDE file
              spkrec.inc for the correct record length.

Parameters

     None.

Exceptions

     1)  If an error occurs while looking up SPK data, the error is
         signaled by a routine in the call tree of this routine.

Files

     See argument HANDLE.

Particulars

     See the SPK Required Reading file for a description of the
     structure of a data type 20 (Chebyshev polynomials, velocity
     only) segment.

Examples

     The data returned by the SPKRnn routine is in its rawest form,
     taken directly from the segment. As such, it will be meaningless
     to a user unless he/she understands the structure of the data type
     completely. Given that understanding, however, the SPKRxx
     routines might be used to "dump" and check segment data for a
     particular epoch.


     C
     C     Get a segment applicable to a specified body and epoch.
     C
           CALL SPKSFS ( BODY, ET, HANDLE, DESCR, IDENT, FOUND )

     C
     C     Look at parts of the descriptor.
     C
           CALL DAFUS ( DESCR, 2, 6, DCD, ICD )
           CENTER = ICD( 2 )
           REF    = ICD( 3 )
           TYPE   = ICD( 4 )

           IF ( TYPE .EQ. 20 ) THEN
              CALL SPKR20 ( HANDLE, DESCR, ET, RECORD )
                  .
                  .  Look at the RECORD data.
                  .
           END IF

Restrictions

     None.

Literature_References

     None.

Author_and_Institution

     N.J. Bachman       (JPL)
     J. Diaz del Rio    (ODC Space)
     I.M. Underwood     (JPL)

Version

    SPICELIB Version 1.0.1, 14-APR-2021 (JDR)

        Edited the header to comply with NAIF standard. Moved SPK
        required reading from $Literature_References to
        $Required_Reading section.

    SPICELIB Version 1.0.0, 17-JAN-2014 (NJB) (IMU)